1. Field of the Invention
The present invention relates to a controlling device and a method for charging a battery for an electric vehicle. More particularly, the present invention relates to a controlling device and a method for charging a battery for an electric vehicle that may finish charging by sensing a full-charging state of the battery.
2. Description of the Related Art
Generally, an electric vehicle is an electric motor-driven-engine different from the general vehicle using gasoline or gas. It may adequately cope with exhaust gas regulations of every country which protect against environmental pollution because it does not emit exhaust gas.
In the electric vehicle, the second battery supplying continuous power so as to drive an engine can be used semipermanently by recharging.
However, in charging the battery, when a charging current continuously flows into the battery despite the full-charging state, a negative characteristic occurs.
Specifically, the battery voltage reduces, and the durability and efficiency of the battery deteriorates, because of a large amount of heat generated in the battery.
In a conventional technique, to solve the above problem, if the battery is fully charged, charging will be completed by detecting a charging end state of the battery in accordance with each charging method.
In the general method of charging the battery, there are a constant current charging method and a constant current/constant voltage charging method.
In the above constant current charging method, the charging end state is generally sensed by a temperature cut-off (TCO) method, a flat time limiting method and a voltage drop (- V) method.
As to the TCO method, since it is dangerous for the temperature of the battery to be raised excessively in the constant current charging, the TCO method controls charging the battery in accordance with the charging limit temperature determined by the specification on the charging limit temperature provided by a manufacturing company. In this method, it is desirable to determine the charging limit temperature considering that if the temperature of the battery is high, the efficiency of the charging battery is improved.
As to the voltage drop (- V) method, in the constant current charging, the battery produces the maximum voltage and causes the voltage drop phenomenon by rejoining with the internal gas. In this method, charging the battery is controlled by the optimum voltage drop value obtained by experiment.
As to the flat time limiting method, in the constant current charging, when the voltage drop value is not detected because it is sensitive to environmental circumstances, a detection limit time of the voltage drop value is determined in case charging should continue. When the voltage drop value is not detected during the above detection limit time of the voltage drop value, charging of the battery will be finished.
In the constant current/constant voltage charging method, the TCO method and a charging current limit method are generally used for sensing the charging state of the battery.
As to the above charging current limit method, after a predetermined current is charged in the constant current charging mode, if the constant current charging mode is transformed into the constant voltage charging mode, a great amount of charging current flows initially. However, as time goes by, the charging current is reduced. In this case, if the charging current is less than a particular value, charging the battery will be finished.
As described above, the conventional methods for sensing the charging end state are separately used. Therefore, when the temperature, the current and the voltage applied to each method are not sensed, the durability and efficiency of the battery is deteriorated because the charging end state is not accurately sensed.